Monitoring device

ABSTRACT

In order to produce a monitoring device for checking for a predefined position of a body or checking for the presence of a body, comprising a pivotal check element, a motor for driving the checking element and a housing for accommodating the motor, which will be universally employable especially in difficult working surroundings, it is proposed that a seal be arrangement between the checking element and the housing around a shaft by means of which the checking element is driven.

[0001] The invention relates to a monitoring device for checking for apredefined position of a body or for checking for the presence of abody, comprising a pivotal checking element, a motor for driving thechecking element and a housing for accommodating the motor.

[0002] Monitoring devices of this type are known from DE 30 03 431 C2,DE 43 10 872 A1 or DE 196 08 628 A1.

[0003] They are employed in machine tools for example in order to checkwhether a body, such as a drill, is still in its predefined position or,has not broken off. They can also be employed for checking as to whethera body has entered a region in which it should not be. Such apenetration would constitute a disturbance in the system which isdetectable by the monitoring device.

[0004] Monitoring devices are subject to the prevailing workingconditions especially when employed in machine tools. In particular,they may be subjected to working fluids such as coolants or lubricantsand/or to waste materials from the operation such as swarf. To this end,it is proposed in DE 43 10 872 A1 that there be provided a double-lippedseal which seals the passage through an end-face cover on the housingfor a shaft.

[0005] Based upon this state of the art, the object of the invention isto provide a monitoring device of the generic kind which, in particular,is employable universally and variably and which enables the operationto be as free from disturbance as possible even in “difficult” workingconditions.

[0006] In accordance with the invention, this object is achieved in amonitoring device of the type described hereinabove in that a seal isarranged between the checking element and the housing around a shaft bymeans of which the checking element is driven.

[0007] Such a seal in accordance with the invention prevents workingfluids or swarf or other impurities from penetrating into the regionbetween the shaft and the checking element and/or between the shaft andthe housing. Metal swarf may, for example, become trapped between thehousing and the checking element in such a manner as to hinder therotation of the shaft. Such processes will interfere with the operationof the monitoring device i.e. it will not be able to perform its realtask, checking for a predefined position of a body or checking for thepresence of a body. The seal arranged in accordance with the inventionwill prevent metal swarf, in particular, from reaching the shaft andthereby producing such a hindrance to the rotational movement. Inaddition, since an additional seal is provided, the sealing of thehousing relative to the exterior space will be improved. The monitoringdevice in accordance with the invention will thereby be less susceptibleto disturbances and the downtime, in which the operation of themonitoring device is interrupted and hence it can no longer perform itsreal task, will be much reduced.

[0008] Moreover, metal swarf can perforate the seal between the passagefor the shaft in the housing whereby fluids can enter into the interiorof the housing. The seal provided in accordance with the inventioncompletely prevents metal swarf from reaching the passage seal.

[0009] It is particularly very advantageous if the seal abuts thechecking element and abuts the housing. The intrusion of swarf and/orfluids into the region between the checking element and the shaft and/orbetween the housing and the shaft is thereby prevented.

[0010] It is advantageous for the seal to be formed symmetrically aboutan axis and especially about a rotational axis of the shaft. Asubstantially angle-independent frictional moment can thereby beobtained, especially during the rotational movement of the checkingelement, thereby achieving simpler control and regulation of the pivotalmovement of the checking element.

[0011] It is particularly very expedient if the seal is then seatedbetween the checking element and the housing co-axially relative to theshaft.

[0012] It is expedient for an intermediate space to be formed betweenthe shaft and the seal. Consequently, the seal itself does not abut onthe shaft and will not hinder its rotational movement.

[0013] In an advantageous variant of an embodiment, provision is madefor the seal to be rotationally fixed relative to the checking element.The seal is thus carried along by the checking element during thepivotal movement of the checking element whilst it will rotate relativeto the housing. Basically, it is also conceivable for the seal to berotationally fixed relative to the housing and then to rotate thechecking element relative to the seal. However, the proposed variant ismore expedient from a constructional point of view since a seal must beprovided around the shaft in the housing in order to seal the passagefor the shaft through the housing. The corresponding annular space isnot available for the arrangement of a mounting element for the sealbetween the checking element and the housing. By contrast, a furtherseal for the checking element itself does not need to be provided apartfrom the seal between the checking element and the housing.

[0014] Expediently, the checking element comprises a mounting elementfor the seal onto which the latter is adapted to be put in order to fixit non-rotationally relative to the checking element. An easilymanufacturable, easily releasable but nevertheless sealed connectionbetween the seal and the checking element in accordance with theinvention can thereby be achieved in a simple manner.

[0015] From a manufacturing point of view it is particularly expedientif the mounting element is formed by a mounting ring through which theshaft is guided and onto which the seal is adapted to be put. The sealcan thereby be arranged completely around the shaft in a simple manner.

[0016] Furthermore, it is expedient to provide an annular recess foraccommodating the seal between the mounting element and the checkingelement. An abutment face for an end-face of the seal is made availableby such an annular recess, and in addition, the seal can rest in fullarea contact around an outer surface of the mounting ring. The seal isthus connected to a large surface area of the checking element so that agood sealing effect is thereby achieved.

[0017] Expediently, the outer diameter of the seal substantiallycorresponds to the diameter of the checking element so that, firstly, alarge abutment face for the seal is available on the checking elementand secondly, material will not be wasted unnecessarily.

[0018] It is particularly very expedient if the seal comprises a packingring for the purposes of pushing it onto the checking element. Goodsealing properties between the seal and the checking element areachieved by virtue of such a packing ring.

[0019] Furthermore, it is particularly very advantageous if the sealcomprises a collar having a V-shaped sealing lip which abuts thehousing. Good sealing properties are achieved between the seal and thehousing by virtue of such a sealing lip, and the spacing between thechecking element and the housing can be varied by means of the sealinglip without the need to provide a plurality of seals for this purpose,since, to a certain extent, the V-shaped sealing lip allows the axialextent with reference to the direction of the rotational axis to be set.

[0020] It is expedient if the collar is rotatable with the checkingelement relative to the housing.

[0021] In order to obtain good sealing properties between the seal andthe housing on the one hand, and in order to be able to vary the axialspacing between the checking element and the housing on the other, it isadvantageous if the outer surface of the collar is substantially in theform of a truncated cone at least when force is not being appliedthereto in the axial direction. An imaginary cone peak of the V-shapedcollar points towards the checking element. Thus, when the axial spacingbetween the checking element and the housing becomes smaller, the collarcan spread in a radial direction so that the effectiveness of the sealwill not worsen despite the change in this spacing.

[0022] It is expedient if the inner surface of the collar is in the formof a truncated cone at least when force is not being applied thereto inthe axial direction. This ensures that the sealing lip will be in fullarea contact with the housing even when the spacing between the checkingelement and the housing becomes smaller thereby achieving good sealingproperties.

[0023] It is expedient if an axial extent of the seal can be varied bythe collar so that the monitoring device in accordance with theinvention can be employed in variable manners and is particularlyeconomical.

[0024] It is especially very advantageous if a control device isprovided by means of which the pivotal position and/or the speed and/orthe torque of the checking element are controllable. The monitoringdevice in accordance with the invention can thereby be employeduniversally. It is particularly advantageous if the control devicecontrols the pivotal position, the speed and the torque of the checkingelement in combination.

[0025] It is expedient if the pivotal movement is controllable by thecontrol device such that the torque lies below a predefined value.Delicate tools such as fine drills for example are employed in machinetools. In the event that a checking element strikes such a tool with ahigh level of torque, it can happen that this tool will be destroyed,for example a very fine drill may break off. Due to the control of thetorque, and especially due to the control of a torque limitingarrangement, it is ensured that the checking element will strike such atool with reduced force whereby the tool will not be destroyed. On theother hand however, the checking element should reach a monitoringregion, in which the predefined position of a body is to be detected orin which a “foreign body” may be expected, as quickly as possible. Tothis end, a high torque must be exerted on the checking element so as toquickly pass through this capture region. Due to the control of thetorque limit, it then becomes possible for the checking element to pivotquickly through a certain region whilst allowing a tool to be struck“gently” by the checking element.

[0026] It is particularly advantageous if the checking element isadapted to be pivoted commencing from a starting position through atransition region into a monitoring region in which the predefinedposition of the body lies or in which the presence of a body should bemonitored, and the predefined value for the maximum permissible torquein the monitoring region is reduced relative to that in the transitionregion. It is thereby possible to quickly pivot through the transitionregion with a high torque value whilst ensuring that the checkingelement will strike the body in the monitoring region with a smalleramount of torque and also ensuring that, when its pivotal movement ishalted by the body and it continues to press against the body, the forceexerted on the body will not be so large as to lead to the destructionof the body.

[0027] Provision is expediently made for the motor to be an electricmotor and for the process of limiting the maximal permissible amount oftorque to be effected by limiting the supply of current to the motor. Ina dc motor, the level of current applied to the motor determines thetorque thereof. A limitation in regard to the maximum permissible amountof torque of the checking element can then be achieved in a simplemanner, and in particular, in an easily controllable manner by limitingmotor current.

[0028] It is especially very advantageous for the speed of the checkingelement to be reducible during its passage from the transition regioninto the monitoring region. It is thereby possible for the checkingelement to pass quickly through the transition region whilst ensuringthat a body being detected in the monitoring region will only be struckgently.

[0029] It is expedient if the reduction of the maximum permissibleamount of torque is effected after the reduction in the speed of thechecking element. It is thereby ensured that the checking element willhave a certain predetermined speed, and in particular, a reduced speedin the monitoring region. Too early a reduction of the torque limitcould counteract this.

[0030] It is expedient if the transition region comprises anacceleration region in which the speed of the checking element isincreased commencing from the starting position so as to enable thetransition region to be quickly passed through. Furthermore, it isexpedient if the transition region comprises a braking region in whichthe speed of the checking element is reduced so as to obtain a reductionin speed in the monitoring region.

[0031] Furthermore, it is advantageous for the speed of the checkingelement in the transition region to be maintained substantially constantbetween an acceleration region and a braking region of the transitionregion. The control and regulation in particular of the pivotal movementof the checking element is improved by maintaining it constant in such amanner. A linear relationship between the pivotal angle and the timeprevails in the region in which a substantially constant speed ismaintained. The corresponding relationships in the acceleration regionand the braking region are non-linear thereby leading to acorrespondingly greater computational effort and greater imprecision. Inaddition, adjustment to a predefined speed ramp is easier to achieve ifthe speed is substantially constant. Inaccuracies in the control processare thereby reduced.

[0032] It is also expedient if the speed of the checking element ismaintained substantially constant in the monitoring region. Inparticular, the arrival at a predefined position can thereby be detectedin a simple manner. Such maintenance of a constant speed is naturallyonly in regard to the checking element not yet having reached theposition of the body being monitored or not yet having reached adisturbing body in the monitoring region.

[0033] The control device expediently comprises a digital angletransmitter for controlling and regulating the pivotal movement of thechecking element. In particular, this may be an incremental transmitter.The rotational angle and the rotational speed of the checking elementover an appropriate time interval can then be defined and preciselycontrolled in a simple manner.

[0034] It is expedient if the control of the speed and the torque of thechecking element is effected by the control device by means oftime-dependent control of the position of the checking element.Basically, the position and speed of the checking element can also becarried out by means of a time-dependent control of the acceleration.However, integration steps are needed for the latter, whereas in thecase of the control of the position of the checking element more easilycalculable differentiation steps can be carried out by formingquotients.

[0035] It is expedient if the control device defines the pivotalposition of the checking element and, furthermore, if the control devicedefines the speed of the checking element. This can be done in a simplemanner with the aid of the digital angle transmitter if the latter givesrise to a pivotal movement through a certain angular range in a certaintime interval. It is especially very advantageous if the control devicedefines the pivotal position and the speed of the checking elementthereby achieving a simple controlling for the pivotal movement of thechecking element.

[0036] It is expedient if the control device is able to undergo alearning cycle for detecting the monitoring region. By virtue of such alearning cycle, it can be determined where the predefined position ofthe body lies and the monitoring region can thereby be limited. Themonitoring device in accordance with the invention thereby automaticallydetermines the region wherein the torque limit must be reduced.

[0037] It is particularly very advantageous if the monitoring region isset by the control device such that it begins at a certain angularamount prior to the learned position in which a body was detected in thelearning cycle. This angular amount may, for example, be 5° or 10° orthe like. This makes for great ease of operation, and it is ensured thatthe checking element will pass quickly through the transition region,whereas the speed will be reduced in the monitoring region and, inparticular, the torque in the monitoring region will be so low that,when a sensing needle on the checking element strikes against a bodythat is to be detected thereby, there will be no consequential damagethereto.

[0038] It is especially very expedient for stop means to be provided forlimiting the pivotal movement of the checking element. The monitoringdevice then has an internal reference position which is unalterable.

[0039] Expediently, for the purposes of moving the checking element intothe reference position, the checking element is moved at a predefinedspeed into a stop position in which corresponding stop means touch oneanother. Such a reference position can be detected in a simple manner.

[0040] It is particularly very advantageous if, for the purposes ofdefining the reference position of the checking element in the stopposition, corresponding stop means are rotated against one another atlow torque. It is thereby possible to define the reference position in avery secure and unambiguous manner.

[0041] Further features and advantages of the invention form the subjectmatter of the following description taken in conjunction with thesketched illustration of the embodiment.

[0042] In the drawing:

[0043]FIG. 1 shows a perspective view of a sensing head for themonitoring device in accordance with the invention;

[0044]FIG. 2 a side view of a seal between a checking element and ahousing for the sensing head, wherein no axial pressure is being exertedon this seal;

[0045]FIG. 3 the seal of FIG. 2, wherein an axial pressure is beingexerted on the seal;

[0046]FIG. 4 a block circuit diagram of a control device for themonitoring device in accordance with the invention;

[0047]FIG. 5 a schematic illustration of the timing course for the speedand the torque of the checking element in a transition region and amonitoring region and

[0048]FIG. 6 a schematic illustration of the pivotal position of thechecking element in the transition region and the monitoring region;

[0049] An embodiment of a monitoring device in accordance with theinvention comprises a sensing head bearing the general reference 10which is shown in perspective in FIG. 1. This has a cylindrical housing12 having a reception space 14 formed in its interior. The housing 12 isprovided with an outer thread 16 on its outer surface, nuts 18 beingscrewable onto said thread. The monitoring device can be positioned, forexample, in a machine tool using these nuts 18.

[0050] The reception space 14 serves for accommodating an electric motor20, this being, in particular, a dc motor. This electric motor 20comprises a shaft 22 which is arranged co-axially with respect to theaxis 24 of the housing 12 which is thus the rotational axis of the shaft22.

[0051] Stop means are provided for limiting the rotational movement ofthe shaft 22. In the embodiment illustrated in FIG. 1, a ring 26 issituated on the shaft 22, said ring being provided with a radiallyoutwardly pointing pin 28. The electric motor 20 itself comprises ahousing 30 and a further pin 34 is arranged on an end-face 32 of thishousing 30 through which the shaft 22 enters, said pin being fixed tothe housing in non-rotational manner whence it is also non-rotationalrelative to the housing 12 of the monitoring device 10 and is parallelto but spaced from the axis 24. When the pin 28 abuts the pin 34, thenthe rotational movement of the shaft 22 in the direction of the pin 34is limited thereby.

[0052] The electric motor 20 is provided with terminal leads 36 whichare connected to a digital angle transmitter 38 (see FIG. 4) and fromthere, they extend to a plug. In this variant of an embodiment, thedigital angle transmitter 38 is disposed in the reception space 14.

[0053] The housing 12 of the sensing head 10 comprises an end-face 40which is provided with a passage opening for the shaft 22 of theelectric motor 20. A seal, which prevents penetration of foreign bodiesor working fluids into the housing 12, is seated in the passage opening(not shown in the Figure).

[0054] The reception space 14 is closed at its end remote from theend-face 40 by a closure element 42 which is preferably in the form of aclosure stopper. The closure element 42 has an internal thread 44 intowhich a plug 46 provided with electrical terminals 48 can be screwed.The terminal leads 36 are connected to the electrical terminals 48. Aconnecting cable 84 (FIG. 4) leads from the plug 46 to a controlapparatus bearing the general reference 49 in FIG. 4. This controlapparatus incorporates, at least in part, a control device 50 forcontrolling and regulating the monitoring device.

[0055] A checking element 52, which is pivotal by the shaft 22, isseated on the shaft 22. This checking element 52 comprises a cylinderelement 54, which is provided with a central recess 56 through whichthis cylinder element 54 can be seated on the shaft 22. The cylinderelement can be fixed to the shaft 22 by clamping screws 58. A sensingneedle 60 having a stop body 62 at its front end is arranged on thecylinder element 54 transversely to the rotational axis 24 and, inparticular, perpendicularly thereto (i.e. in a radial direction). Thissensing needle 60 is limited by said stop body 62 when the shaft 22rotates.

[0056] The cylinder element 54 comprises an annular mounting element 64facing the shaft 22 around the recess 56, the internal diameter of saidmounting element corresponding substantially to the diameter of therecess 56 but the outer diameter thereof being reduced relative to thatof the cylinder element 54. An annular recess 66 is thereby formedbetween the mounting ring 64 and the cylinder element 54 of the checkingelement 52.

[0057] A seal 68 is adapted to be put onto the mounting ring 64, saidseal being arranged around the shaft 22 between the housing 12, inparticular, its end-face 40, and the checking element 52 in order toprevent penetration of fluids and impurities, such as saw or drillingswarf for example, into the region between the checking element and thehousing 12. For this purpose, the seal 68 abuts on both the cylinderelement 54 and the end-face 40 of the housing 12. An intermediate space69 is formed between the seal 68 and the shaft 22 so that the shaft 22does not directly abut the seal 68.

[0058] As is shown in FIGS. 2 and 3, the seal 68 comprises a packingring 70 which is adapted to be put onto the mounting ring 64. The outerdiameter of this packing ring 70 substantially corresponds to the outerdiameter of the cylinder element 54 and the inner diameter thereofsubstantially corresponds to the outer diameter of the mounting ring 64,and it is preferably selected to be somewhat smaller so that the seal 68forms a non-rotational friction-fit on the mounting ring 64 when it hasbeen put into place.

[0059] A collar 72 having a sealing lip 74 of V-shaped cross-section isconnected to the packing ring in one piece manner. Provision may be madefor an intermediate ring 76 to be arranged between the collar 72 and thepacking ring 70.

[0060] When the seal is not subjected to an axial force, the sealing lip74 has a substantially truncated-cone-shaped outer surface 78 as shownin FIG. 2, and the imaginary cone peak points towards the checkingelement 52. The inner surface 80 of the collar 72 is likewisesubstantially in the form of a truncated cone, and the angle of the conefor the inner surface 80 is smaller than that for the outer surface 78.

[0061] By virtue of such a construction, it is ensured that the sealingeffect between the checking element 52 and the housing 12 can beachieved even in the case of differing spacings between this checkingelement 52 and the end-face 40 of the housing 12. As is shown in FIG. 3,the collar 72 can be compressed and hence the sealing lip 74 will spreadoutwardly when it is subjected to an axial force (i.e. when the checkingelement 52 is displaced towards the end-face 40 of the housing 12).Since said sealing lip continues to abut on the end-face 40, the sealingeffect is maintained even when the spacing between the checking element52 and the housing 12 is varied. The seal 68 remains on the end-face 40over an end region comprised by the inner surface 80 due to thetruncated-cone-shaped construction of the inner surface 80.

[0062] During a pivotal movement of the checking element relative to thehousing 12, the seal 68, which is held by the mounting ring 64 so as torotate with the checking element 52, rotates relative to the housing 12.The shaft 22 is located completely within an inner space 82 of the seal68 comprised by the packing ring 70 and the collar 72. This means thatthe shaft 22 is sealed relative to the exterior by the seal 68.

[0063] As is shown in FIG. 4, the control device 49 is connected via theconnecting cable 84 to the sensing head 10. The electric motor 20 issupplied with electrical energy via this connecting cable 84.Furthermore, the control unit 50 supplies control and regulating signalsto the digital angle transmitter 38, which, in turn, controls theelectric motor 20.

[0064] The control device 50 incorporates a current supply means 86which comprises terminals 88 a, 88 b for an energy source. Provision ismade, for example, for a voltage of 24 volts to be applied between theterminals 88 a and 88 b. An EMC filter 92 is arranged between thecurrent supply means and a microcontroller 90 so as to absorb orcompensate for electromagnetic disturbances.

[0065] Furthermore, there is provided a switch, especially a rotaryswitch 94 for a pivotal angle of the checking element 52 which isconnected to one input of the microcontroller 90. (In FIG. 4, the inputsof the microcontroller 90 are indicated by arrows pointing towards itand the outputs are indicated by arrows pointing away therefrom.) Apivotal angle for the checking element 52 is defined by means of thisrotary switch.

[0066] A further input of the microcontroller 90 is provided with achangeover switch 96, which is used for switching between a toolmonitoring operation for checking for a predetermined position of abody, or a free space monitoring operation for checking for the presenceof a body.

[0067] Switching between a clockwise or an anticlockwise pivotalmovement can be effected by a further changeover switch 98.

[0068] Furthermore the microcontroller 90 is connected to a non-volatilestore 100, for example, an EEPROM, in which certain pivotal positions ofthe checking element 52 can be stored so that the microcontroller canresort to them during the operation of the monitoring device inaccordance with the invention.

[0069] An output of the microcontroller 90 is connected to a motordriver 102 for the electric motor 20. An EMC filter 104 for absorbing orcompensating for electromagnetic interference is located between themotor driver 102 and the electric motor 20. The electric motor 20 isconnected to the EMC filter 104 via the connecting cable 84.

[0070] The digital angle transmitter 38 is connected via this EMC filter104 to an intelligent transducer 106, which, in turn, is connected via afilter 108 to the microcontroller 90. The microcontroller 90 can thusevaluate the signals from the digital angle transmitter 38, which areconveyed to the electric motor 20, and hence determine, in particular,the instantaneous position, speed and acceleration of the checkingelement 52.

[0071] The microcontroller 90 has a “Start” input 110, which causes themonitoring operation to begin when a signal is applied thereto. An inputprotection means 112 is arranged between this input 110 and themicrocontroller so as to absorb input signals which could lead todestruction of the microcontroller.

[0072] A “learning” input 114 is also provided and this is likewiseconnected via the input protection means 112 to the microcontroller 90.When this input 114 has a signal applied thereto, a learning cycle isstarted in which the checking element 52 learns the predefined positionof a body (tool monitoring process).

[0073] Furthermore, the microcontroller 90 comprises three outputs 116,118, 120 which are connected to an output driver 122 from which theoutput signals of the monitoring device are derivable. A signal isthereby derivable from a first output 124 “OK” of this output driver 122which indicates that the monitoring process has been correctly carriedout and that no disturbances have been found (i.e. that during the toolmonitoring process, the body was detected at its predefined position, orthat during the free space monitoring process, no body was detected inthe monitoring region).

[0074] A signal is derivable from a second output 126 “nOK” indicatingthat the monitoring process has run successfully but that a disturbancewas detected, i.e. either the body was not at its predefined position(tool monitoring process) or the presence of a body was detected in themonitoring region (free space monitoring process).

[0075] The output driver 152 has a third output 128 “FAULT” whichindicates that the monitoring process has not been successful. Thereason for this may, for example, be that impurities such as swarf haveinterfered with the rotational movement of the shaft 22. However, thereare a variety of other reasons that could have led to a disturbance inthe monitoring operation.

[0076] In order to indicate the result of the monitoring process in anoptical manner, the microcontroller 90 also has an output 130 which isconnected to an LED 132 which turns green if the monitoring process hasrun successfully and no disturbances were detected. Another terminal 134is provided which is connected to an LED 136 which gives out a red lightif the monitoring process has run successfully but a disturbance wasdetected in the sense that the body was not at its predefined position(tool monitoring process), or that a body is present in the monitoringregion (free space monitoring process). A terminal 138 is connected toan LED 140 which emits an optical signal (for example a yellow light) ifthe control device 50 has established that an error occurred during themonitoring process.

[0077] The operation of the monitoring device in accordance with theinvention proceeds as follows:

[0078] After the control device 50 has been switched on, the shaft isslowly rotated until the stop means 28 and 34 abut one another, i.e. thepins 28 and 34 strike one another. A reference position is thereby set.The pin 28 is then pressed against the pin 34 by a small amount oftorque so as to reset the zero position again. The microcontroller 90then reads the position of the switches 94, 96 and 98. If the rotaryswitch 94 occupies a wrong or unsuitable switching position (for examplethe pivotal angle 0°), then the step of pressing the pin 28 against thepin 34 with a low level of torque and the reading of the switchpositions is repeated. If the rotary switch 94 is in a suitableposition, it is checked as to whether the switch 96 is set for the toolmonitoring mode (detection of a body at a predefined position) orwhether the free space monitoring mode (detection of a body in amonitoring region) is set via the switch 96. In the event that the “freespace monitoring” mode is set, then the corresponding start input isinterrogated. In the event that the “tool monitoring” mode is set, thenthe “learning” input 114 will be interrogated and a learning process maythen be initiated. Following a successful learning process, the “Start”input 110 for the tool monitoring process is interrogated and a toolmonitoring operation is carried out in correspondence therewith. If theinterrogation indicates that the learning process was not successful,then the step, in which the pins 28 and 34 are pressed together at a lowtorque level for setting the reference position, is passed over and thecorresponding successive steps mentioned above are executed.

[0079] A learning (teach in) cycle proceeds as follows:

[0080] The microcontroller 90 first checks as to whether the “learning”input 114 is active. If the check is positive, then the pivotal angleset via the rotary switch 94 is checked once again. If the pivotal angle0° is set then it is not possible to learn anything. The blockingposition 0° is stored in the store 100 and the checking element isslowly pivoted back into its starting position (reference position).

[0081] In the event of a pivotal angle setting not equal to 0°, then thechecking element is pivoted at a slow speed to the angle set via therotary switch 94 and it is checked, with the intervention of a timedelay step, as to whether the checking element and the sensing needle 60have reached a position switch which indicates the end of a monitoringregion. Should the arrival at this position switch be detected, thenthis means that there was no obstacle in the set range and hence that ablocking position could not be learnt. The blocking position zero isthen stored in the store 100 and the checking element is slowly pivotedback into the reference position.

[0082] If, during the check as to whether the checking element 52 hasreached the position switch, it is determined that the checking elementwas pivoted beyond a permissible range (it is for this reason that thetime delay step is utilised), then this means that the obstacle liesoutside the permissible range. The blocking position zero is then storedin the store 100 and the checking element 52 is slowly pivoted back intothe reference position.

[0083] In the positive event that the checking element 52 lies in thepermissible range, then the learning process was successful and theinstantaneous position of the checking element 52 represents theposition of the obstacle, i.e. the predefined position of the body.Thereafter, the checking element 52 is likewise slowly pivoted back intothe reference position.

[0084] The tool monitoring process then proceeds as follows:

[0085] Firstly, it is checked as to whether the “Start” input 110 isactive. Each of the LEDs 132, 136 and 140, and the outputs 124, 126 and128 are then switched off. Thereafter, it is checked as to whether 0° isstored as a learned position in the store 100. If this is the case, thenthis means that it is not possible to effect the sensing operation asthe position has not been learnt successfully and consequently nosensing is carried out. Signals are applied to the outputs 126 “nOK” and128 “Fault”.

[0086] In the event that a learned position not equal to 0° has beendetermined, the checking element 52 is pivoted through a transitionregion 142 (FIGS. 5 and 6) and it is checked as to whether a specificmaximum time has expired. In the event that this maximum time hasexpired, the LEDs 136 and 140 are switched on, the checking element 52is returned at high speed to its reference position, and signals areapplied to the outputs 126 and 128. The expiry of the time limit can becaused, in particular, by the fact that curls of swarf are hindering orblocking the movement of the sensing needle 60.

[0087] In the event that it is registered that the time limit has stillnot expired, the checking element is pivoted into a monitoring region144. It is then checked once more, as to whether a time limit hasexpired. If this is the case, then a disturbance has occurred in themonitoring device and the LEDs 136 and 140 are switched on again in anappropriate manner, and signals are applied to the outputs 126 and 128.If this time limit has not expired, then the whole of the monitoringregion will be traversed, whereafter, at the end of the monitoringregion, it is checked as to whether the checking element is still withinthe permissible pivotal angle range. If this is not the case, then thiswill be due to the fact that a body is not located in the monitoringregion. The LED 136 “NOK” is then switched on, the checking element 52is pivoted back at high speed into its reference position and signalsare applied to the “nOK” output 126. Signals are not applied to the“FAULT” output 128 since the monitoring process has been properlyeffected, but no body has been detected in the monitoring region 144.

[0088] In the event that the checking element 52 is located in apermissible pivotal angle range, the LED 132 is switched on and signalsare applied to the “OK” output 124, although signals are not applied tothe outputs 126 and 128.

[0089] The traversal of the transition region 142 and the monitoringregion 144 will be described in more detail hereinbelow.

[0090] If the free space monitoring process has been set via thechangeover switch 96, i.e. the check as to whether a body is present inthe monitoring region, then it is firstly rechecked as to whether the“START” input 110 is active. If this check proves positive, then theLEDs 132, 136 and 140 and the outputs 124, 126 and 128 are switched off.If the pivotal angle position set via the rotary switch is 00, thenmonitoring is not possible and the LEDs 132, 136 and 140 remain switchedoff. The checking element 52 is then pivoted back to its referenceposition, insofar as it is not already there, and signals are applied tothe “FAULT” output 128.

[0091] If the set position differs from 0°, then the checking element 52passes through the transition region 142 and the monitoring region 144,as will be explained in more detail hereinbelow, and it is checked as towhether the checking element 52 is still within the permissible range.If this is not the case, then this means that a body is present in themonitoring region 144 whereby the “OK” LED 132 remains switched offwhereas the “nOK” LED 136 is switched on. The checking element is thenpivoted back into its reference position and signals are applied to the“nOK” output 126, whereas the other two outputs 124 and 128 do notreceive signals.

[0092] By contrast however, if the checking element 52 is in thepermissible range, then this means that no body was present in themonitoring region 144. Consequently, the LED 132 is switched on, thechecking element is pivoted back into its reference position and signalsare applied to the “OK” output 124, whilst signals are not applied tothe outputs 126 and 128.

[0093] The control device 50 controls/regulates the position, thepivotal speed and the torque of the checking element 52 and its sensingneedle 60 via the microcontroller 90 and the digital angle transmitter38. To this end, the motor current through the electric motor 20 iscontrolled in order to control the torque thereof, and the voltageapplied to the electric motor 20 is controlled in order to control therotation of the shaft 22 by means of the digital angle transmitter 38.In particular, provision may be made for the microcontroller 90 toproduce a pulse width modulated signal, which contains informationregarding the position control/regulating process as well as the momentcontrol/regulating process.

[0094] Basically, the transition region 142 serves for the purpose ofallowing the checking element 52 to be rapidly moved into the monitoringregion 144 commencing from a starting position (reference position). Theactual detection process for checking for the predetermined position ofa body or for checking for the presence of a body takes place in themonitoring region 144.

[0095] The torque of the electric motor 20, with which the latter iseffective via the shaft 22 on the checking element 52, is detefined bythe amount of current applied to this dc motor. The microcontroller 90sets this current to be such that the maximum possible torque 146, whichlimits the torque of the checking element 52 and which is sketched bymeans of the dashed lines in FIG. 5, is reduced in the monitoring region144 relative to the transition region 142. This thereby prevents thesensing needle 60 of the checking element 52 from striking a body whichit is trying to detect with a high level of torque or from exerting acorrespondingly high force on the body should this be present in thepivotal path of the sensing needle 60.

[0096] A speed curve 148 representing the pivotal speed of the checkingelement 52 is shown in FIG. 5 in a schematic manner. Commencing from thereference position 150, the transition region 142 comprises anacceleration region 152 in which the checking element is accelerated,i.e. its speed is increased from zero up to an essentially constantvalue. The speed is kept substantially constant in a region 154following this acceleration region, whereafter the speed is reduced to alower value than that in the region 154 in a braking region 156 i.e. thechecking element 52 is braked. The monitoring region 144 adjoins thebraking region 156. The transition point 158 between the braking region156 and the monitoring region 144 lies at a predetermined angularposition prior to the predefined position of the body (in the case ofthe tool monitoring process), for example, in an angular range of 10°prior to this predefined position.

[0097] The torque limit is reduced during the transition from thebraking region 156 into the monitoring region 144, preferably within ashort time interval after the transition point 158. It is therebyensured that there is a sufficiently large torque for pivoting thechecking element 52 in the monitoring region 144 at a substantiallyconstant lower speed; on the other hand, it is also ensured therebythat, over the greater part of the monitoring region 144, the maximumpossible torque 146 is reduced relative to that in the transition region142.

[0098] If there is no body in the monitoring region 144, the checkingelement 52 will be pivoted through the whole of the monitoring region144 at a substantially constant speed, as is indicated by the section160 of the curve in FIG. 5. Should the end 162 of the monitoring region144 be reached, then the checking element 52 is pivoted rapidly backinto the reference position 150, and the checking element is braked forthe purposes of reversing the direction of rotation and is thenaccelerated in the counter direction.

[0099] If there is a body in the monitoring region 144, then thechecking element 52 will be braked within a very short period of timefrom its substantially constant speed 164 down to zero, as is indicatedby the section of the curve 166. Thereafter, the checking element 52 canbe quickly pivoted back into the reference position 150.

[0100] The variation in torque is illustrated by the curve 168 in FIG.5. A high level of torque, which lies below the maximum torque level146, is exerted in the acceleration region 152 so as to accelerate thechecking element up to a constant speed from the reference position 150.This torque is higher than the frictional moment exerted via the seal 68so as to produce a net acceleration.

[0101] In the course of the transition into the region 154, the motortorque is reduced by appropriately reducing the motor current so as toobtain a constant speed for the checking element 52. The torque thencorresponds substantially to the frictional moment. The torque isreversed in the braking region 156 in order to thereby brake thechecking element 52. In essence, such reversal only occurs in thebraking region 156. During the transition 148, the torque is increasedagain and held at a value which is somewhat lower than that in the range154.

[0102] Should the checking element 52 reach the body, then the torquewill rise since the microcontroller 90 registers the slowing down of thechecking element and tries to compensate for it. This rise, which isindicated by 170 in FIG. 5, can be attributed, inter alia, to the factthat the control processes cannot occur instantaneously, but rather,need a certain transient time. However, due to the provision of thetorque limiting arrangement in accordance with the invention, via whichthe torque is reduced in the monitoring region 144, the torque of thechecking element 52 will be prevented from exceeding its maximumpermissible value despite the rise 170.

[0103] In conjunction with the drop in speed 166 to zero and/or the risein the torque level, a control signal will then be produced by themicrocontroller 90 thereby causing the direction of the torque to bereversed so as to quickly pivot the checking element 52 back into thereference position 150.

[0104] In the event that there is no body in the monitoring region 144against which the sensing needle 60 can strike, the constant torque ismaintained up to the end 162 of the monitoring region so as to obtain asubstantially constant speed for the checking element 52, and, at theend 162 of the monitoring region, the torque is reversed so as torapidly conduct the checking element 52 back again into the referenceposition 150 (this is not shown in FIG. 5).

[0105] Commencing from the reference position 152, the pivotal path 172of the checking element 52 is shown plotted against time in theschematic illustration in FIG. 6. Commencing from its reference position(the zero position), the pivotal angle increases non-linearly in theacceleration region 152 whereas, in the region 154, the pivotal anglerises substantially linearly due to the constant speed. Then, due to thebraking action, the rise becomes more gradual than linear in the brakingregion 156 and then reverts to rising linearly in the monitoring region,although this rise is more gradual than that in the region 154. If thebody is reached at the pivotal angle 174, then this pivotal angle doesnot alter in time for as long as the pivotal direction is not reversed.This reversal is indicated by the section 176 of the curve.

[0106] In the event that the sensing needle 60 does not meet a body, thechecking element 52 will pass through the whole of the monitoring region144, the pivotal movement then being reversed at the end 162 thereofwhereby the pivotal angle will become smaller again. The path-time curvefor the reverse pivoting process when returning to the referenceposition 150 extends in a corresponding manner.

[0107] The angle of rotation within a specified time interval (a timeincrement) can be defined with the aid of the digital angle transmitter38 which is an increment transmitter. The pivotal position of thechecking element 52 is known to the microcontroller at every moment intime, as is also, at least to a first approximation, the instantaneousspeed thereof in the form of a differential quotient betweencorresponding path intervals and time intervals. The torque can bedetermined by the motor current.

[0108] Predetermined control and regulating curves for the position, thespeed and the torque can be stored, for example, in a discrete form intables in the store 100. The microcontroller 90 compares the actualvalues with the stored values. In the event of deviations therefrom, themotor driver 102 is controlled accordingly so as to ensure that thepivotal movement of the checking element 52 will closely follow thepredefined curves. The curves shown in FIGS. 5 and 6 correspond to thosecurves predefined in tabular form, i.e. they represent the controlledvalues.

What is claimed is:
 1. A monitoring device for checking for a predefinedposition of a body or for checking for the presence of a body,comprising a pivotal checking element (52), a motor (20) for driving thechecking element (52) and a housing (12) for accommodating the motor(20), characterised in that a seal (68) is arranged between the checkingelement (52) and the housing (12) around a shaft (22) by means of whichthe checking element (52) is driven.
 2. A monitoring device inaccordance with claim 1, characterised in that the seal (68) abuts onthe checking element (52) and abuts on the housing (12).
 3. A monitoringdevice in accordance with claim 1, characterised in that the seal (68)is formed symmetrically about an axis (24).
 4. A monitoring device inaccordance with claim 1, characterised in that the seal (68) is seatedbetween the checking element (52) and the housing (12) co-axiallyrelative to the shaft (22).
 5. A monitoring device in accordance withclaim 1, characterised in that an intermediate space (69) is formedbetween the shaft (22) and the seal (68).
 6. A monitoring device inaccordance with claim 1, characterised in that the seal (68) is adaptedto be rotationally fixed relative to the checking element (52).
 7. Amonitoring device in accordance with claim 6, characterised in that thechecking element (52) comprises a mounting element (64) for the seal(68) onto which the latter is adapted to be put in order to fix itnon-rotationally on the checking element (52).
 8. A monitoring device inaccordance with claim 7, characterised in that the mounting element (64)is formed by a mounting ring through which the shaft (22) is guided andonto which the seal (68) is adapted to be put.
 9. A monitoring device inaccordance with claim 7, characterised in that an annular recess (66)for accommodating the seal (68) is formed between the mounting element(64) and the checking element (52).
 10. A monitoring device inaccordance with claim 1, characterised in that an outer diameter of theseal (68) substantially corresponds to the diameter of the checkingelement (52).
 11. A monitoring device in accordance with claim 1,characterised in that the seal (68) comprises a packing ring (70) forthe purposes of putting it onto the checking element (52).
 12. Amonitoring device in accordance with claim 1, characterised in that theseal (68) comprises a collar (72) having a V-shaped sealing lip (74)which abuts the housing (12).
 13. A monitoring device in accordance withclaim 12, characterised in that the collar (72) is rotatable with thechecking element (52) relative to the housing (12).
 14. A monitoringdevice in accordance with claim 12, characterised in that the outersurface (78) of the collar (72) is substantially in the form of atruncated cone at least when force is not being applied thereto in theaxial direction.
 15. A monitoring device in accordance with claim 14,characterised in that an imaginary cone peak of the collar (72) pointstowards the checking element (52).
 16. A monitoring device in accordancewith claim 14, characterised in that the inner surface (80) of thecollar (72) is substantially in the form of a truncated cone at leastwhen force is not being applied thereto in the axial direction.
 17. Amonitoring device in accordance with claim 12, characterised in that anaxial extent of the seal (68) can be varied by the collar (70).
 18. Amonitoring device in accordance with claim 1, characterised in that acontrol device (50) is provided by means of which the pivotal positionand/or the speed and/or the torque of the checking element (52) arecontrollable.
 19. A monitoring device in accordance with claim 18,characterised in that the control device (50) controls the pivotalposition, the speed and the torque of the checking element (52) incombination.
 20. A monitoring device in accordance with claim 18 or 19,characterised in that the pivotal movement is controllable by thecontrol device (50) in a manner such that the torque will lie below apredefined value (146).
 21. A monitoring device in accordance with claim20, characterised in that the checking element (52) is adapted to bepivoted commencing from a starting position (150) through a transitionregion (152) into a monitoring region (144) in which the predefinedposition of the body lies or in which the presence of a body should bemonitored, and the predefined value for the maximum permissible torque(146) in the monitoring region (144) is reduced relative to that in thetransition region (142).
 22. A monitoring device in accordance withclaim 20, characterised in that the motor (20) is an electric motor andthe limiting of the maximum permissible torque (146) is effected bylimiting the supply of current to the motor.
 23. A monitoring device inaccordance with claim 21, characterised in that the speed of thechecking element (52) is reducible during its transfer from thetransition region (142) into the monitoring region (144).
 24. Amonitoring device in accordance with claim 23, characterised in that thereduction of the maximum permissible torque (146) is effected after thereduction in the speed of the checking element (52).
 25. A monitoringdevice in accordance with claim 21, characterised in that the transitionregion (142) comprises an acceleration region (152) in which the speedof the checking element (52) is increased commencing from the startingposition (150).
 26. A monitoring device in accordance with claim 21,characterised in that the transition region (142) comprises a brakingregion (156) in which the speed of the checking element (52) is reduced.27. A monitoring device in accordance with claim 21, characterised inthat the speed of the checking element (52) in the transition region(142) is maintained substantially constant between an accelerationregion (152) and a braking region (156) of the transition region (142).28. A monitoring device in accordance with claim 21, characterised inthat the speed of the checking element (52) is maintained substantiallyconstant in the monitoring region (144).
 29. A monitoring device inaccordance with claim 1, characterised in that the control device (50)comprises a digital angle transmitter (38) for controlling the pivotalmovement of the checking element (52).
 30. A monitoring device inaccordance with claim 29, characterised in that the controlling of thespeed and the torque of the checking element (52) is effected by thecontrol device (50) by means of the time-dependent controlling of theposition of the checking element (52).
 31. A monitoring device inaccordance with claim 29, characterised in that the control device (50)sets the pivotal position of the checking element (52).
 32. A monitoringdevice in accordance with claim 29, characterised in that the controldevice (50) sets the speed of the checking element (52).
 33. Amonitoring device in accordance with claim 30, characterised in that thecontrol device (50) sets the pivotal position and the speed of thechecking element (52).
 34. A monitoring device in accordance with claim21, characterised in that the control device (50) is adapted to undergoa learning cycle for determining the monitoring region (144).
 35. Amonitoring device in accordance with claim 34, characterised in that themonitoring region (144) is set by the control device (50) such that itbegins at a certain angular amount prior to the learnt position at whicha body is detected in the learning cycle.
 36. A monitoring device inaccordance with claim 1, characterised in that stop means (28, 34) areprovided for limiting the pivotal movement of the checking element (52).37. A monitoring device in accordance with claim 36, characterised inthat, for the purposes of setting a reference position (150) of thechecking element (52), this is moved at a predefined speed into a stopposition (150) in which corresponding stop means (28, 34) touch.
 38. Amonitoring device in accordance with claim 37, characterised in that,for the purposes of defining the reference position (150) of thechecking element (52) in the stop position, corresponding stop means(28, 34) are rotated against each other at low torque.